1. Field of the Invention
The present invention relates to a holographic stereogram.
One of the technologies now being widely researched with the aim of visually reproducing stereoscopic images is holographic stereograms. Holographic stereograms are comprised of an array of a plurality of element holograms. Each of these element holograms is loaded with a unique modulation value corresponding to the stereoscopic image to be reproduced. By irradiating these element holograms with coherent light, the stereoscopic image is visually reproduced.
2. Description of the Related Art
As explained later in detail, the conventional methods for calculating the modulation values (pattern) to be loaded to the element holograms to realize a computer generated one-dimensional holographic stereogram are:
(a) The method using Fourier series expansion and PA1 (b) The method of using discrete Fourier transform by making discrete the distribution of intensity of diffraction light with respect to the angle (angle from the center of an element hologram to points in a block AB).
If finding the modulation values by the above-mentioned conventional methods by performing a Fourier transform or discrete Fourier transform, in general since the Fourier transform (F(.omega.)) of (x) is expressed by ##EQU1## not only the real component, but also the imaginary component appears. The same holds true for both one-dimensional and two-dimensional holographic stereograms.
Therefore, if trying to faithfully reproduce the distribution of intensity of diffraction light, it is necessary that the display device not only be able to perform modulation of the amplitude (amplitude modulation), but also be able to perform modulation of the index of refraction (phase modulation). Accordingly, there is the first problem that the drive system of the display device becomes complicated.
Further, in general, in a Fourier transform, it is known, the converted energy exists up to the higher order terms. As a result, there is the second problem that it becomes difficult to establish the condition (assumption) of the "point of sight being sufficiently far compared with the size of the element hologram" and therefore faithful reproduction of the distribution of intensity of diffraction light is inhibited.